Thursday 27 January 2011 19.32 EST
First published on Thursday 27 January 2011 19.32 EST

Like Martin, I heard about the astrologers' petition to the BBC and blogged about it, together with another astrology-related story that recently hit the headlines. Unlike him, I was critical of the knee-jerk response of many scientists, science writers and fans of science. I also had some quibbles about his post, so I'd like to start by thanking him for hosting this – and, before you leap to the comments section, making it clear that I do not believe in astrology. However, I do believe that a little knowledge and understanding can help the cause of science communication far more than ridicule.

As is well known to readers of The Lay Scientist, the Astrological Association, prompted by remarks made by Brian Cox and Dara O'Briain, has asked for "fair and balanced representation" (note, not "equal representation"). This has resulted in widespread derision from those who can see nothing wrong with stating that "astrology is rubbish" and "nonsense". Most, however, have failed to understand exactly what has annoyed these astrologers, or to take the time to find out what astrology actually is.

You may feel that there is no need to understand something that you know is rubbish, but anyone who makes a statement about it on television or in a national newspaper should know what they're talking about. Anyone who is interested in making the lay public understand what science offers, and what astrology does not, needs to be informed and open to discussion. They need to be able to explain that astrology fails because its hypothesis – that the positions of the planets can influence or give information about earthly events and personalities – has not been demonstrated.

The Astrological Association is not complaining about a statement such as this. Rather, they consider it unfair that they are represented as having no knowledge of the astronomy and celestial mechanics that Cox and O'Briain are paid to explain on TV. They are annoyed that astrology is considered to consist solely of those who read and write newspaper horoscopes. Serious astrologers often have an excellent understanding of, and respect for, astronomy. They are, in fact, a not insignificant audience for astronomy programmes, lectures and books. This is why, as I explained in my earlier post, stories about "changing zodiac signs" and the "13th sign" Ophiucus do no one any favours. While Parke Kunkle's "revelation" might confuse those with little knowledge of astrology or astronomy, it comes as no surprise to anyone else. The effect of precession has been understood for centuries, and practising astrologers are more than capable of dealing with this recurrent attack.

Which brings me to the history: a little historical understanding should make astronomers and science communicators realise that practising astrologers are likely to have good knowledge of planetary motions. Up until the late 17th century, astrology and astronomy were deeply interconnected. Since then there has been a parting of ways, but astrologers have continued to make use of accurate astronomical data. Astrology is not so much the father of positional astronomy and celestial mechanics as its client, patron and midwife.

However, perhaps worse than complete ignorance of history, is the danger of its being misused or misrepresented. While Martin has assured me that he is aware that astrology was dominant in the pre-modern world, this is not what his readers are likely to have picked up. Instead he points to an instance in which a medieval astronomer appears to have spoken out against astrology suggesting that it was "already being ridiculed in the Dark Ages". This is, consciously or unconsciously, something that many others have done: keen to distance themselves from astrology, astronomers have leapt on examples of apparently 'scientific' disdain for the practice.

This radically misreads the historic context and is as ignorant or dishonest a tactic as that used by proponents of Intelligent Design who mine Darwin's writings for useful quotes. It is also a dangerous line for science communicators to take: the astrologers probably know their history better. Note that Nicholas Campion, a university lecturer and author of a recent and well-received history of astrology, is also a past president of the Astrological Association. Historians of astronomy know that before the late 17th century there are far more examples of astronomers who were astrologers or directly supported astrology than not (let's try Ptolemaeus, Peuerbach, Regiomontanus, Apian, Copernicus, Rheticus, Tycho, Kepler and Galileo for starters). In addition, when someone appears to speak against astrology, as the 14th-century example linked by Martin, they were nearly always only aiming at parts of astrology – such as divination or casting natal horoscopes – usually for theological or political rather than scientific reasons.

This sub-division of astrology is not usually recognized, but the casting of horoscopes is part of judicial astrology, while 'natural astrology' includes things like bodily health, weather and the planting, harvesting or failure of crops. The latter tradition is, perhaps, a little easier to understand from a modern perspective; after all, we know that celestial bodies (the Sun and Moon) affect climate, tides, meteorology and biology. In the 17th century there were serious attempts to test the validity of various aspects of astrology. They failed, and astrology, which had been taught in universities across Britain and Europe, lost its place in the elite intellectual sphere.

Astrology as a scientific hypothesis has been put to the test and found wanting: it is this that should be the focus of commentary by science communicators. Practising astrologers should be prepared to accept this kind of evidence, but they will continue to complain, with some justification, if they are presented as idiots who don't understand precession and do nothing but write newspaper horoscopes that cover around a twelfth of the population in one go.

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Guest post by Dr Rebekah Higgitt, Curator of History of Science and Technology, National Maritime Museum and Royal Observatory, Greenwich.